The invention relates to a steering device for a motor vehicle having a steering wheel, which is connected in a rotationally rigid manner to a steering shaft, which is hollow from end to end and through which at least one electrical conductor is guided in order to make an electrical connection with control units on the steering wheel side.
In particular, it relates to a steering device of the flexible steering concept (FSC design type) without any mechanical drive connection between the steering wheel and a steering gearbox. The steering device also has a hydraulic default level, which includes a hydraulic feed unit, coupled to the steering wheel, and a hydraulic actuating unit, which is coupled to the steering gearbox. In the event of a malfunction, the hydraulic actuating unit can also be used to produce a wheel steering angle by an input from the steering wheel.
With respect to the relevant prior art, in particular relating to the FSC design type, reference is made to DE 10 2008 021 973 A1. A steering device as described above is disclosed in German utility model no. 1 698 768.
The so-called FSC systems, in which the steering request input by the driver of a vehicle at the steering wheel or the like (instead of a steering wheel, a so-called side stick or the like can also be provided as the so-called steering control element, and for the sake of simplicity only one steering wheel is discussed below) is not transmitted to the steerable wheels of the vehicle by the direct mechanical route (that is, as in the case of the aforementioned DE 1 698 768 and in conventional modern vehicles) and by way of the so-called steering column or the steering shaft as well as a steering gearbox coupled thereto (for example, a rack and pinion steering gearbox), but rather by an electric or hydraulic route, are advantageous with respect to the configuration possibilities for the system components in the vehicle. Since, however, an actuator, which is actuated by signals of the steering wheel input and, as a result, pivots the steerable wheels, can fail, these systems provide a so-called default level, which in view of a desired installation flexibility is usually configured hydraulically and can include such features as a hydraulic feed unit, which is coupled to the steering wheel, and a hydraulic actuating unit, which is coupled to the steering gearbox, as well as a hydraulic circuit, which hydraulically connects together these two units.
Furthermore, an FSC system has to have a so-called steering torque simulator, with the aid of which a torque, directed opposite to the steering torque generated by the driver, can be applied to the steering wheel. This is done in order to give the driver a typical steering feeling and, thus, a quasi-tactile contact with the road lane. In particular, an end stop is also provided for the rotational movement of the steering wheel that corresponds to the maximum steering angle of the steerable vehicle wheels. This end stop is typically represented by the steering torque simulator, in that an electric motor, which forms this steering wheel simulator, applies such a high counter-torque to the steering torque, generated by the driver, that the driver cannot turn the steering wheel any further.
The pertinent prior art also includes flexible conductor tracks, highly flexible cables and flat conductor ribbon cables, which have proven to be reliable as flexible transmission systems for electric current between movable elements having electrical connections. The disclosures of DE 10 2005 016 676 A1 and EP 1 713 096 B1, both of which describe such conductors, are incorporated herein by reference to the extent required for the invention with respect to the pertinent prior art.
Due to the operating elements and safety devices, such as an airbag, placed directly at the steering wheel, it is necessary to transmit information and power electrically from the stationary vehicle parts into the rotatable steering wheel and back. Such a transmission has to be possible while at the same time it must also be possible to rotate the steering wheel out of its central position, in order to turn the wheel as far as to the predetermined steering stops, by way of multiple revolutions in each direction. At the same time, the function of smooth action, low noise and at low cost over the entire lifetime of the motor vehicle has to be ensured and, in particular, at least for one electrical line, but typically for a large number of electrical lines, having a cross section for current strength of up to 8 amperes. For example, it may be easily necessary to run 16 electrical lines into the steering wheel. Moreover, most vehicles have an adjustable steering wheel with height and length adjustment, where the length adjustment changes the distance to the driver. To this end, the steering column may be designed in such a way that it can be telescoped. In addition, the aim is to minimize the necessary installation space and to simplify the assembly process and still maintain a reliable, fast installation into and removal from the motor vehicle.
The aforesaid necessitates the object of the present invention, which is to provide a steering device and a method for making an electrical connection with the equipment on the steering wheel side, so that both the steering device and the method can meet, based on the aforementioned prior art, the above described requirements.
According to the invention, a steering device for a motor vehicle with a steering wheel, which is connected in a rotationally rigid manner to a steering shaft, which is hollow from end-to-end and through which at least one electrical conductor is guided, in order to make an electrical connection with the equipment on the steering wheel side, is characterized by the fact that the conductor, in particular a flexible conductor track, highly flexible cables, and/or flat conductor ribbon cables, is guided in an axial direction through the entire steering shaft and emerges from the steering shaft at both ends of the steering shaft and is surrounded in essence by a protective device, in particular, by two protective tubes, the length of which can be changed in the axial direction, in particular, by moving the protective tubes in and out in a telescopic manner.
This approach has the advantage that when the amount of installation space required is extremely small in the radial direction, the electrical connection can be designed adequately long, a feature that prevents the electrical connection from failing because of the voltage load on the conductors owing to the rotation of the steering wheel, where such a voltage load is generated over the customary useful life of a motor vehicle. The longer the conductors can be chosen, the more this load (because of the rotatability of the steering wheel by three to five revolutions) decreases for the conductors that run centrally in the steering shaft. Due to the length and the shape of the conductors and the longitudinally adjustable protective device, a telescopic adjustment of the steering column can also take place. In addition, the conductors are housed in the hollow steering shaft in such a way that they are protected and, at the same time, use space in the steering shaft that is not needed for other usages. In comparison to a conventional coil spring cartridge, costs and installation space are saved; and also the design freedom in the upper steering wheel region is increased.
A preferred embodiment of the invention provides that the protective device includes two tubes, an outer and an inner tube, which can be slid inside one another in the manner of a telescope with their adjacent end. This arrangement has the advantage that the longitudinally adjustable protective device is simple in design and easy to manufacture, for example, of a synthetic plastic material. If then the tubes of the protective device can be secured to one another in the axial and in the circumferential direction, in particular, in the axially totally extended position, it is possible in a simple way to implement without additional parts the transport securing mechanism that prevents the two tubes from turning in relation to each other, for example, in the central position for driving straight ahead, in a pre-assembled unit. Such a pre-assembled unit can include at least one end module, an additional end module, the conductor with the electrical connectors and the protective device, connecting the end modules, where the protective device consists of two tubes, which can be slid inside one another in the manner of a telescope in the axial direction and are secured to one another by anti-rotation and anti-displacement securing devices. Due to the anti-displacement securing device in the as-delivered state, it is possible to avoid an uncontrolled turning of the spiral cable with the conductors, thus eliminating the possibility of damaging the cable before and after installation. The tubes of the protective device can be secured to one another in a friction locking and/or positive locking manner, for example, by use of a bayonet lock or by way of a serration in the circumferential direction, combined with at least one snap cam, in particular a latching collar, in the axial direction. If the friction locking and/or positive locking connection of the tubes of the protective device can be released by hand at least from one end of a tube on the steering wheel side, this arrangement has the advantage that the assembly or disassembly of the central cable unit in the steering column is very simple and also easy to repeat because of the locking possibility.
Advantageous embodiments of the invention are characterized by the fact that on the end of the protective device that faces away from the steering wheel, the conductor is held, in particular, fixed in the axial and radial direction, by way of an end module, which does not turn with the steering shaft; and on the end of the protective device that faces the steering wheel, the conductor is held, in particular, fixed in the axial and radial direction, by an additional end module that turns with the steering shaft. As a result, the twistable length of the conductor can be chosen longer than the length of the steering shaft, in that the length of the conductor between the two end modules is greater than their distance from one another. This feature can be achieved in that the conductor is constructed in the axial direction at least inside the shaft in the form of a spiral, in a corrugated manner, in the form of an accordion, in the form of a helix, in the form of a ribbon, and/or as a single cable. The conductor can be fixed in a simple way in its position in the closed protective housing by way of the end modules. At the same time, in order to connect the conductor to its corresponding terminals at the steering wheel and on the vehicle side, it is advantageous to attach the cable connectors to the ends of the conductor. These cable connectors can be plug-in connectors. In order to insert the plug-in connectors with the conductors into the steering shaft, all of them have to fit through the steering shaft or, more specifically, through the protective device. If, at the same time, the size of the plug-in connectors is as large as possible, then the requirement can be satisfied best if the conductors are provided with a large number of electrical plug-in connectors that are axially offset along the conductors such that they lie individually one after the other. Furthermore, a plurality of conductors can be accommodated on a conductor carrier in such a way that they are electrically insulated from one another. This conductor carrier can be designed, for example, as flexible conductor tracks, highly flexible cables and/or as a flat conductor ribbon cable. It is also possible to accommodate a plurality of such conductor carriers with electrically insulated conductors, for example, lying one above the other, together at least in the steering shaft. In this case it is advantageous if one or both end modules fix the conductor or, more specifically, the conductor carriers at least in the axial direction, in particular, however, also in the radial direction.
For a steering device that is characterized by the fact that it does not have a mechanical drive connection between the steering wheel and a steering gearbox, especially if the steering gearbox is driven by an actuator that is acted upon with the output signals from the steering wheel actuation, such an arrangement of at least one conductor in the steering shaft is especially advantageous. It is also possible to implement an electrically controlled steering of a flexible steering concept, FSC, in a simple and cost saving way, in that the steering gearbox is coupled to a hydraulic actuating unit, which is acted upon by a hydraulic feed unit that is controlled by the steering wheel, and forms in the event of a malfunction of the actuator a default level for controlling the steering by way of a hydraulic connection between the hydraulic feed unit and the hydraulic actuating unit that can be switched into the hydraulic circuit.
It is advantageous for a simple and reliable installation if those embodiments of the steering device, in which a unit can be pre-assembled, include, furthermore, at least one end module, an additional end module, a protective device and conductors, in particular, also with plug-in connectors. Then, such a unit can be easily moved from the pre-assembled state into the assembled state in the motor vehicle, if the unit has the anti-torsion securing device, which fixes the position of the end module to the additional end module at least in the torsional direction and, in particular, in essence in a central position, based on a torsion capability of the conductor in both directions, a straight ahead driving position of the steering wheel. This central position ensures that in any case the conductor can be turned in both directions with the steering wheel as far as up to its stop. The two tubes can be fixed in relation to each other in the circumferential direction in an advantageous manner.
For the installation of the pre-assembled unit on the vehicle side and for the installation of the steering wheel it is advantageous if the electrical plug connections are made automatically during the mounting process. In that regard, on the vehicle side or, more specifically, the steering wheel side the plug-in connectors make the connection from the conductor to the terminals in the vehicle or, more specifically, in the steering wheel. In particular, this is done in the course of bringing the pre-assembled unit into the steering wheel, when the end module is attached permanently to the vehicle and in the course of mounting the steering wheel, when the additional end module is connected in a rotationally rigid manner to the steering shaft.
According to the invention, there is also provided a method for making an electrical connection with the equipment on the steering wheel side in a steering device of a motor vehicle, with a steering shaft, which is hollow from end to end and through which at least one electrical conductor is guided, in particular a flexible conductor track, highly flexible cables and/or flat conductor ribbon cables, in a pre-assembled unit comprising at least one end module, an additional end module, the conductor with electrical connectors and a protective device. The protective device connects the end modules and consists of two tubes, which can be slid inside one another in the manner of a telescope in the axial direction and are secured to one another by an anti-rotation and anti-displacement securing device. The method includes at least the following assembly steps:
(a) inserting the pre-assembled unit with tubes, which are secured to one another, in the axial direction into the hollow steering shaft until the end module is placed in such a way that it is permanently attached to the vehicle by a positive lock;
(b) releasing the anti-rotation and anti-displacement securing device between the two tubes of the protective device;
(c) sliding in a telescopic manner the protective device as far as the stop on the steering wheel bottom and securing the additional end module in such a way that it is fixed on the steering wheel; and
(d) electrical contacting of the electrical connectors with their corresponding terminals.
Particular embodiments of the method may include, as described above, advantageously individual features of the subject matter of the invention. One particularly advantageous method is characterized, for example, by the fact that the electrical connectors are secured on the vehicle in such a way that they are aligned with the corresponding electrical connectors on the end module of the pre-assembled unit, so that their electrical connection is made automatically at the same time that the positive lock on the end module is produced when the pre-assembled unit is inserted into the hollow steering shaft.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.